a) Field of the Invention
The invention is directed to a water jet propulsion unit for watercraft with a pump and a stator and a nozzle for generating a propulsive water jet and with control elements for changing the direction of the water jet.
b) Description of Related Art
There are many known examples of water jet propulsion units for watercraft in which the water which is sucked in via a pump and accelerated exits as a directed jet via a nozzle which influences its direction, turbulence being eliminated in the water jet via a stator.
For example, U.S. Pat. No. 4,992,065 shows a water jet propulsion unit having a nozzle which is arranged downstream of the stator and supported so as to swivelable about a vertical axis. The outlet opening of the nozzle can be changed via flaps which are swivelable about an axis oriented horizontally thereto until the direction of the water jet is reversed for the purpose of controlled movement in reverse.
A construction of this kind is extremely costly due to the control elements, poses considerable sealing problems for the accelerated water jet, and causes a substantial cross-sectional portion of the water jet to be cut off, in particular when deflecting angles are large. As a result of these deflection losses, the reverse thrust is reduced in such a way that maneuvering problems occur especially through passes having currents and in narrow harbors. Further, a corresponding steering effect must be allowed for; otherwise, a reversing of the directional effect takes place when changing from forward to reverse motion which further complicates the control elements and leads to errors.
Simpler constructions, e.g., in the form of two flaps which are arranged downstream of the outlet opening and are swivelable respectively about vertical axes (see GB 1 190 735), result in a totally unsatisfactory steering effect of the water jet propulsion unit when stopped and at slow speed.
To prevent flow losses it is also known to construct the nozzle serving as a control from concentrically supported spherical surfaces. This is also costly and requires complicated controlling and sealing elements--see DE 26 44 743 A1.
For the above reasons, there is a substantial need for improvement of such water jet propulsion units for the controlled forward and reversing motion of a watercraft of whatever kind.